Illumination and plasma light sources

Abstract

An illumination source and plasma light source are provided that overcome the shortcomings of conventional approaches. In a laser-sustained plasma (LSP) broadband source plasma lamp, an illumination source for igniting and sustaining a plasma includes one or more ignition lasers configured to ignite a plasma in a gas contained within the plasma lamp. The illumination source further includes one or more sustain lasers configured to sustain the plasma. The illumination source includes a delivery optical fiber and one or more optical elements configured to selectively optically couple the output of the one or more ignition lasers and the output of the one or more sustain lasers into the delivery optical fiber.

Description

[Technical field]

[0001] The present invention relates to illumination sources and plasma light sources. [Background technology]

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62 / 236,904, filed October 4, 2015, entitled “NOVEL LAMP IGNITION SCHEME AND LAMP DESIGN FOR LASER PUMPED LAMPS USED ON BRIGHTFIELD WAFER INSPECTION TOOLS,” with Anant Chimmalgi, Rudolf Brunner, Anatoly Shchemelinin, Ilya Bezel, Erik Kim, Rajeev Patil as inventors, and is incorporated herein by reference in its entirety.

[0003] There is an ever-increasing need for improved illumination sources for use in the inspection of ever-smaller semiconductor devices. One such illumination source is the laser-sustained plasma source. Laser-sustained plasma (LSP) sources are capable of generating high-power broadband light. Laser-sustained sources work by focusing laser radiation into a gas volume to excite a gas, such as argon or xenon, into a plasma state capable of emitting light. This action is commonly referred to as "pumping" the plasma. Plasma lamps typically require electrodes to ignite the plasma, which is then sustained only by laser energy. The use of electrodes also requires complex glass-to-metal sealing techniques and complex bulb-form factors. The complex bulb shape is prone to stress concentrations and defects in the metal-glass seal, which can reduce the overall burst pressure and strength of the lamp. The electrodes themselves are also prone to degradation and sputtering, which reduces the glass transmittance with dimming. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2014 / 0240951 Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to provide a system and method that overcomes the shortcomings of conventional approaches as discussed above. [Means for solving the problem]

[0006] An illumination source for electrodeless ignition of plasma in a broadband plasma source is disclosed in accordance with one or more embodiments of the present disclosure. In one embodiment, the illumination source includes one or more ignition lasers configured to ignite a plasma in a gas contained within the plasma lamp. In another embodiment, the illumination source includes one or more sustaining lasers configured to sustain the plasma. In another embodiment, the illumination source includes a delivery optical fiber. In another embodiment, the illumination source includes one or more optical elements configured to selectively optically couple the output of the one or more ignition lasers and the output of the one or more sustaining lasers to the delivery optical fiber. In another embodiment, the illumination source is integrated into a broadband laser-sustained plasma (LSP) source, whereby one or more lamp optics direct the output from the delivery optical fiber to a predetermined volume of gas within the plasma lamp to ignite and sustain a plasma in the predetermined volume of gas within the plasma lamp.

[0007] An illumination source for electrodeless ignition of a plasma in a broadband plasma source is disclosed according to one or more alternative embodiments of the present disclosure. In one embodiment, the illumination source includes one or more ignition lasers configured to ignite a plasma in a gas contained within the plasma lamp. In another embodiment, the illumination source includes one or more sustain lasers configured to sustain the plasma. In another embodiment, the illumination source includes a delivery optical fiber having an input, the output of the one or more sustain lasers being coupled to the input. In another embodiment, the illumination source includes a process optical fiber. In another embodiment, the illumination source includes a fiber coupler optically coupled to the output of the delivery optical fiber and the input of the process optical fiber. In another embodiment, the fiber coupler includes one or more optical elements configured to selectively optically couple the output of the one or more ignition lasers and the output of the one or more sustain lasers to the input of the process optical fiber. In another embodiment, the illumination source is integrated into a broadband laser-sustained plasma (LSP) source, whereby one or more lamp optics direct the output from the process optical fiber to a volume of gas in the plasma lamp to ignite and sustain a plasma in the volume of gas in the plasma lamp.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. [Brief description of the drawings]

[0009] Many advantages of the present disclosure may be more fully understood by those skilled in the art by reference to the following drawings. [Figure 1A] FIG. 1 is a schematic diagram of a system for forming a light-sustained plasma in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram of an illumination source including a sustain laser and an internal ignition laser in accordance with one or more embodiments of the present disclosure. [Figure 1C] FIG. 1 is a schematic diagram of an illumination source including a sustain laser and an internal ignition laser in accordance with one or more embodiments of the present disclosure. [Figure 1D] FIG. 1 is a schematic diagram of an illumination source including a sustain laser and an external ignition laser in accordance with one or more embodiments of the present disclosure. [Figure 1E] FIG. 1 is a schematic diagram of an illumination source comprising multiple dichroic mirrors in accordance with one or more embodiments of the present disclosure. [Figure 1F] 1 is a schematic diagram of a system for forming a light-sustained plasma having an external ignition laser positioned along a different direction than the sustaining laser in accordance with one or more embodiments of the present disclosure. [Figure 2A] 1 is a schematic diagram of a plasma lamp having a cylindrical plasma bulb in accordance with one or more embodiments of the present disclosure. [Figure 2B] 1 is a schematic diagram of a plasma lamp having a spherical plasma bulb in accordance with one or more embodiments of the present disclosure. [Figure 2C] 1 is a schematic diagram of a plasma lamp having a cardioid-shaped plasma bulb in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Reference is now made to the details of the disclosed subject matter, as illustrated in the accompanying drawings. While specific embodiments of the present invention have been illustrated, it will be apparent that various modifications and embodiments of the present invention may be made by those skilled in the art without departing from the scope and spirit of the foregoing disclosure. Accordingly, the scope of the present invention is limited only by the claims appended hereto.

[0011] 1A-2C, a system for igniting and sustaining a plasma in a broadband light source according to the present disclosure is described. An embodiment of the present disclosure relates to an electrodeless plasma lamp for use in an LSP broadband source. Another embodiment of the present disclosure relates to a simplified plasma lamp shape and configuration. Such an embodiment increases the reliability, lifetime (by preventing power due to electrode degradation) and scalability of the plasma lamp. Another embodiment of the present disclosure relates to a plasma ignition scheme that includes one or more ignition lasers coupled in-line with one or more sustaining lasers. In these embodiments, one or more ignition lasers may ignite the plasma with a given plasma lamp, and one or more sustaining lasers may sustain the plasma after plasma ignition.

[0012] 1A illustrates a system 100 for forming a light-sustained plasma (LSP) according to an embodiment of the present invention. System 100 may be used as a broadband irradiation source in many applications, including, but not limited to, inspection and metrology tools.

[0013] U.S. Patent No. 7,435,982, issued October 14, 2008, provides a general description of generating light-sustained plasmas, and is incorporated herein by reference in its entirety. U.S. Patent No. 7,786,455, issued August 31, 2010, provides a general description of generating plasmas, and is incorporated herein by reference in its entirety. U.S. Patent No. 7,989,786, issued August 2, 2011, provides a general description of generating plasmas, and is incorporated herein by reference in its entirety. U.S. Patent No. 8,182,127, issued May 22, 2012, provides a general description of generating plasmas, and is incorporated herein by reference in its entirety. U.S. Patent No. 8,309,943, issued November 13, 2012, provides a general description of generating plasmas, and is incorporated herein by reference in its entirety. U.S. Patent No. 8,525,138, issued February 9, 2013, also generally describes plasma generation and is incorporated herein by reference in its entirety. U.S. Patent No. 8,921,814, issued December 30, 2014, also generally describes plasma generation and is incorporated herein by reference in its entirety. U.S. Patent No. 9,318,311, issued April 19, 2016, also generally describes plasma generation and is incorporated herein by reference in its entirety. U.S. Patent Publication No. 2014 / 029154, filed March 25, 2014, also generally describes plasma generation and is incorporated herein by reference in its entirety. U.S. Patent Publication No. 2015 / 0282288, filed March 31, 2015, also generally describes transverse pumping of light-sustained plasma and is incorporated herein by reference in its entirety. Generally, the various embodiments of the present disclosure should be interpreted to extend to any plasma-based light source known in the art. U.S. Patent No. 7,705,331, issued April 27, 2010, provides a general description of optics used in connection with plasma generation, and is incorporated herein by reference in its entirety.

[0014] In one embodiment, the system 100 includes a plasma lamp 110. In another embodiment, the system 100 includes an illumination source 102 configured to ignite and / or sustain a plasma 111 within the plasma lamp 110. The illumination source 102 may emit light having any selected wavelength or wavelength range, such as, but not limited to, infrared, visible light, and / or ultraviolet light. In one embodiment, the illumination source 102 includes one or more sustaining lasers 120 and one or more ignition lasers 130. The one or more ignition lasers 130 may ignite the plasma 111 within the plasma lamp 110. And, once the plasma 111 is ignited, the one or more sustaining lasers 120 function to sustain the plasma 111 within the plasma lamp 110.

[0015] In another embodiment, the system 100 includes one or more optical fibers (e.g., delivery fibers and / or process fibers) for transmitting illumination (e.g., ignition illumination and / or maintenance illumination) from the illumination source 102 to the illumination path 101 of the system 100.

[0016] In another embodiment, the system includes one or more lamp optics. For example, as shown in FIG. 1A, the one or more lamp optics may include, but are not limited to, a focusing element 108 (e.g., an ellipsoidal, parabolic, or spherical mirror) for directing and / or focusing illumination 105 from illumination source 102 (via optical fiber 104) to a volume of gas 109 contained within plasma lamp 110 to ignite and / or sustain plasma 111. Additionally, focusing element 108 may similarly focus broadband illumination 114 emitted by the generated plasma 111 and direct broadband illumination 114 to one or more further optical elements 116.

[0017] In alternative or alternative embodiments, the one or more lamp optics may include a set of illumination optics for directing and / or focusing illumination 105 from illumination source 102 (via optical fiber 104) to a volume of gas contained within plasma lamp 110 to ignite and / or maintain plasma 111. For example, the set of illumination optics may include a set of reflective elements (e.g., mirrors) configured to direct output from process optical fiber 104 to a volume of gas within plasma lamp 110 to ignite and / or maintain plasma 111. Additionally, the one or more lamp optics may include, but are not limited to, a set of focusing elements (e.g., mirrors) for focusing broadband illumination 114 emitted by plasma 111 and directing broadband illumination 114 to one or more further optical elements 116. U.S. Patent Application No. 15 / 187,590, filed June 20, 2016, describes the use of separate illumination and collection optics in plasma sources in a general manner and is incorporated herein by reference.

[0018] It should be noted that the optical configuration used to deliver sustain illumination from one or more sustain lasers 120 and ignition illumination from one or more ignition lasers 130 of illumination source 102 to plasma 111 may include any optical configuration capable of delivering sustain illumination and ignition illumination sequentially or simultaneously to plasma 111 (or gas). For example, the optical configuration used to couple illumination from one or more sustain lasers 120 and illumination from one or more ignition lasers into optical fiber 104 may include reflective and / or transmissive optics. Additionally, the optical configuration may include one or more blocking mirrors, one or more adjustable or flipping mirrors, one or more dichroic mirrors, one or more polarization combiners, etc.

[0019] 1B-1C show an illumination source 102 comprising one or more sustain laser sources and one or more ignition light laser sources in accordance with one or more embodiments of the present disclosure.

[0020] In one embodiment, the illumination source 102 includes one or more sustain lasers 120a, 120b and one or more ignition lasers 130. In one embodiment, the one or more sustain lasers 120a, 120b include one or more continuous wave (CW) lasers. For example, but not limited to, the one or more sustain lasers 120a, 120b of the laser source 102 may include one or more diode lasers (e.g., diode stacks). In another embodiment, the one or more ignition lasers 130 of the laser source 102 include one or more pulsed lasers. For example, but not limited to, the one or more ignition lasers 130 of the laser source 102 may include one or more Q-switched lasers. By way of example, but not limited to, the one or more ignition lasers 130 of the laser source 102 may include one or more Nd:YAG lasers. As another example, the one or more ignition lasers 130 of the laser source 102 may include, but are not limited to, one or more nanosecond pulsed lasers, one or more picosecond pulsed lasers, or one or more femtosecond pulsed lasers. As another example, the one or more ignition lasers 130 may include one or more modulated CW lasers (i.e., CW lasers operating in a modulated mode). As an example, the one or more ignition lasers 130 may include one or more modulated diode lasers.

[0021] In another embodiment, the illumination source 102 includes a delivery fiber 138 for transmitting the optical output of the illumination source (eg, sustain illumination and / or ignition illumination) to one or more downstream optical elements.

[0022] In another embodiment, the illumination source 102 includes a fiber coupler 140. For example, as shown in FIG. 1B, the fiber coupler 140 may optically couple an output of the delivery fiber 138 to an optical input of the process fiber 104. The fiber coupler 140 may include any number or type of optical elements required to couple the output of the delivery fiber 138 to the input of the process fiber 104. For example, the fiber coupler 140 may include a lens 142 and a lens 144 positioned to couple the output of the delivery fiber 138 to the input of the process fiber 104. Additionally, the process fiber 104 may be a sacrificial optical fiber, allowing a user to attach a new fiber to the fiber coupler 140 when needed.

[0023] As an example, the illumination source 102 may include a Q-switched nanosecond pulsed laser for igniting the plasma and one or more diode lasers for sustaining the plasma. In this example, the output of the Q-switched nanosecond pulsed laser may be in-line coupled with the diode laser output within the laser source 102 itself before being coupled to the delivery fiber 138. In one embodiment, the diode lasers 120a, 120b (e.g., diode stacks) may be operated continuously in CW mode, and once the pulsed laser 130 ignites the plasma, the diode lasers 120a, 120b may take over the role of sustaining the plasma. It should be noted that the use of fiber lasers may simplify the design of the laser source, as they are generally more reliable, smaller, and offer more freedom of placement than other options.

[0024] It should be noted that a set of optical elements / components known in the art may be used to couple the output 133 of one or more ignition lasers 130 in-line with the output of one or more sustaining lasers 120a and / or 120b to the input of the delivery fiber 138.

[0025] In one embodiment, a set of mirrors may be used to spatially separate the outputs of lasers 120a, 120b, 130 and to direct and / or focus the outputs of lasers 120a, 120b, 130 to the input of delivery fiber 138. For example, as shown in FIG. 1B, mirrors 126a, 126b, 127, 128 are used to direct laser illumination from sustain lasers 120a, 120b and ignition laser 130 to the input of delivery fiber 138.

[0026] It should be noted that the available space is occupied by the laser illumination 123a, 123b from the sustain lasers 120a, 120b, and one or more optical elements may be used to temporarily block a portion of the sustain laser illumination to allow transmission of the ignition illumination 133 to the delivery fiber 138 and the plasma. For example, as shown in FIG. 1B, a flip mirror 127 (or an actuatable mirror) may be positioned to reflect the ignition illumination 133 to the mirror 128 and delivery fiber 138 during plasma ignition while blocking the sustain illumination 123b from laser 120b. Then, as shown in FIG. 1C, after plasma ignition, the flip mirror 127 may be adjusted so that it blocks the ignition illumination 133 from the ignition source 130 while allowing the sustain illumination 123b to pass to the mirror 128 and delivery fiber 138. Additionally, the light source 102 may include any number of lenses 122 a , 122 b , 132 , 136 to direct and focus the light into the delivery fiber 138 .

[0027] The optical outputs of the one or more sustaining lasers 120a, 120b and the one or more ignition lasers 130 may be coupled to a delivery fiber 138 in a manner known in the art. In another embodiment, the delivery fiber 138 and / or the process fiber 104 may be multi-step or multi-core optical fibers, whereby different wavelengths of light are focused into different layers of a given optical fiber. U.S. Patent Application Serial No. 15 / 274,956, filed September 23, 2016, describes the use of multi-step or multi-core optical fibers in connection with plasma generation, and is incorporated herein by reference in its entirety.

[0028] 1D illustrates an illumination source 102 comprising one or more sustain laser sources and one or more ignition light laser sources in accordance with one or more alternative embodiments of the present disclosure. In this embodiment, ignition illumination 133 may be transmitted to the process fiber 104 via a fiber coupler 140. In one embodiment, the fiber coupler 140 includes one or more dichroic mirrors 148 adapted to reflect the ignition illumination 133 into the process fiber 104 while passing illumination from the sustain lasers 120a, 120b through the delivery fiber 138 to the process fiber 104.

[0029] In one embodiment, dichroic mirror 148 is removable. In this regard, dichroic mirror 148 may be selectively disposed within the fiber coupler for specific applications or upon plasma ignition. By way of example, dichroic mirror 148 may be removed once plasma 111 is ignited.

[0030] This configuration allows the output of an external ignition pulsed laser 130 operating at a different wavelength than the sustain lasers 120a, 120b to be coupled into the process fiber 104 and into the plasma 111. The addition of an external laser (e.g., a fiber laser or a conventional Nd:YAG laser) to the above configuration allows flexibility in increasing the pulsed laser power (pulse energy).

[0031] It should be noted that although the external ignition source of Figure 1D is shown as the only ignition source in Figure 1D, this configuration is not a limitation of the present disclosure. The internal ignition source 130 of Figure 1C and the external ignition source 130 of Figure 1D may be used simultaneously to flexibly increase ignition power in applications requiring high ignition power.

[0032] The optical configurations illustrated in FIGS. 1B-1D are not limited to two sustain lasers or one ignition laser. Rather, the optical configurations illustrated in FIGS. 1B-1D may include any number of sustain lasers and ignition lasers. For example, illumination source 102 may include one or more sustain lasers (e.g., one, two, three sustain lasers, etc.). In this embodiment, the optical configurations of FIGS. 1B-1D may be modified to include another sustain laser. As an example, mirror 128 may be a dichroic mirror that transmits illumination from another sustain laser to lens 136. As another example, illumination source 102 may include one or more ignition lasers (e.g., one, two, three ignition lasers, etc.).

[0033] FIG. 1E illustrates an illumination source 102 comprising one or more sustain laser sources and one or more ignition light laser sources according to one or more alternative embodiments of the present disclosure. In this embodiment, the illumination source 102 includes one or more dichroic mirrors and lasers 120a, 120b, and 130 that emit laser illumination at different wavelengths (or wavelength bands). For example, the first sustain laser 120a emits laser illumination at a wavelength λ1, the second sustain laser 120b emits laser illumination at a wavelength λ2, and the ignition laser 130 emits laser illumination at a wavelength λ3 (where λ1, λ2, and λ3 are different). Additionally, the mirrors 150, 152, and 154 may be dichroic mirrors. In this regard, the mirror 150 may reflect light at a first wavelength λ1 (or set of wavelengths). And the mirror 152 transmits light at the first wavelength λ1 while reflecting light at a second wavelength λ2. Additionally, mirror 154 transmits light at the first wavelength λ1 and the second wavelength λ2 while reflecting light at the third wavelength λ3. In this regard, illumination from one or more sustain laser sources and illumination from one or more ignition light laser sources may be coupled into lens 136, which focuses and / or directs (sequentially or simultaneously) the ignition and sustain illumination into delivery fiber 138. Fiber coupler 140, described herein above, may then couple the output of delivery fiber 138 to the input of process fiber 104, which then transmits the output of light source 102 through various optical elements to the plasma 111 (or gas).

[0034] It should be noted that illumination from sustain lasers 120a, 120b and one or more ignition sources 130 may be combined utilizing polarization-based optical elements. By way of example, a set of polarizing elements (e.g., polarizing beam splitters, polarization combiners) may be used to couple illumination from one or more sustain lasers and illumination from one or more ignition sources into the delivery fiber 138. In this regard, illumination from one or more sustain lasers may be polarized in one state while illumination from one or more ignition lasers is polarized in an orthogonal state. A set of polarizing beam splitters / combiners may then be incorporated in a manner similar to the dichroic mirror of FIG. 1E.

[0035] 1B-1E are not intended to limit the scope of the present disclosure, but are provided for illustrative purposes only. It will be appreciated that any number of equivalent optical configurations may be incorporated to deliver sustain illumination and ignition illumination to the plasma 111, either sequentially or simultaneously.

[0036] FIG. 1F illustrates a system 100 for forming a light-sustained plasma (LSP) according to an alternative embodiment of the present disclosure. In this embodiment, ignition illumination may be delivered to the plasma lamp 110 via an ignition laser 130 arranged to deliver ignition illumination from a different direction than the illumination beam 105. For example, ignition illumination 133 may be coupled to the plasma lamp 110 via a side port 150 of the focusing element 108. Alternatively, ignition illumination 133 may be coupled into the plasma lamp 110 via other directions. It is noted that the electrodeless configuration provides greater versatility when coupling ignition illumination 133 to the plasma lamp 110. Additionally, ignition illumination 133 may reuse all or a portion of focusing element 108 shared with one or more sustaining lasers 120.

[0037] 2A-2C show various bulb shapes that may be used in the plasma lamp 110 of the system 100, in accordance with one or more embodiments of the present disclosure. In one embodiment, the plasma bulb 202 may be cylindrical, as shown in FIG 2A. In another embodiment, the cylindrical plasma bulb 202 may be vertically elongated to help distribute convection currents within the plasma lamp.

[0038] In another embodiment, the plasma bulb 202 may be spherical, as shown in Figure 2B. Note that a spherical plasma bulb 202 can reduce or avoid the need to correct aberrations in the broadband illumination emitted by the plasma 111.

[0039] In another embodiment, the plasma bulb 202 may have a cardioid (heart) shape, as shown in Figure 2C. In one embodiment, the cardioid plasma lamp may have a peak 210 on the inner surface of the glass bulb to direct the convection of the gas 109 in the volume of the plasma lamp 110.

[0040] 2A-2C, the plasma lamp 110 may include a gas port assembly 205 operably coupled to a portion of the plasma bulb 202 of the plasma lamp 110. For example, the plasma lamp 110 may include a gas port assembly 205 mechanically connected to a base of the bulb 202 and configured to selectively facilitate the transfer of gas from a gas source to an interior region of the bulb 202 of the plasma lamp 110.

[0041] In one embodiment, the gas port assembly 205 may include an inlet 207, a supply cap 203, a receiving cap 206, and a clamp 208 suitable for mechanically securing the supply cap 203 to the receiving cap 206. In this embodiment, gas from a gas source (not shown) may be transferred (i.e., flow) from the gas source to the interior volume of the bulb 202 through the inlet 207 of the gas port assembly 205. Additionally, the inlet 207, supply cap 203, receiving cap 206, and clamp 208 may each be constructed from a selected metallic (e.g., stainless steel) or non-metallic material.

[0042] U.S. Patent Application No. 13 / 647,680, filed October 9, 2012, describes the use of refillable gas light bulbs and various bulb shapes, and is incorporated herein by reference in its entirety. While Figures 2A-2C show various plasma light bulb shapes implemented in a refillable light bulb (with a gas port assembly), it should be noted that each of the plasma light bulb shapes described in the present invention may also be implemented in a non-refillable plasma lamp.

[0043] It should be noted that while most of this disclosure focuses on plasma lamps, including plasma bulbs, the scope of this disclosure may extend to, but is not limited to, any gas-containing structure or vessel known in the art of plasma generation, such as a plasma bulb, plasma cell, plasma chamber, etc.

[0044] The use of plasma light bulbs is described in at least U.S. Patent Application No. 11 / 695,348, filed April 2, 2007, U.S. Patent Application No. 11 / 395,523, filed March 31, 2006, and U.S. Patent Application No. 13 / 647,680, filed October 9, 2012, each of which is previously incorporated herein in its entirety. The use of plasma cells is described in at least U.S. Patent Application No. 14 / 231,196, filed March 31, 2014, and U.S. Patent Application No. 14 / 288,092, filed May 27, 2014, each of which is previously incorporated herein in its entirety. U.S. patent application Ser. No. 12 / 787,827, filed May 26, 2010, U.S. patent application Ser. No. 14 / 660,846, filed March 17, 2015, U.S. patent application Ser. No. 14 / 670,210, filed March 26, 2015, and U.S. patent application Ser. No. 14 / 224,945, filed March 25, 2014, describe the use of a gas chamber as a gas containment structure, and each is incorporated herein in its entirety.

[0045] 1A, the transmissive portions (e.g., bulb, transmissive element, or window) of the plasma lamp 110 of the system 100 may be formed from any material known in the art that is at least partially transmissive to the broadband illumination 114 generated by the plasma 111 and / or the illumination 105 from the illumination source 102. For example, the one or more transmissive portions (e.g., bulb, transmissive element, or window) of the plasma lamp 110 may be formed from any material known in the art that is at least partially transmissive to EUV radiation, VUV radiation, DUV radiation, UV radiation, NUV radiation, and / or visible light generated within the plasma lamp 110. Additionally, the one or more transmissive portions of the plasma lamp 110 may be formed from any material known in the art that is at least partially transmissive to IR radiation, visible light, and / or ultraviolet light from the illumination source 102. In another embodiment, one or more transparent portions of the plasma lamp 110 may be formed from any material known in the art that transmits both radiation from the illumination source 102 (e.g., an infrared source) and radiation emitted by the plasma 111 (e.g., EUV, VUV, DUV, UV, NUV radiation and / or visible light).

[0046] In some embodiments, the transmissive portion of the plasma lamp 110 may be formed from a low OH content fused silica glass material. In another embodiment, the transmissive portion of the gas containment structure may be formed from a high OH content fused silica glass material. For example, the transmissive portion of the plasma lamp 110 may include, but is not limited to, SUPRASIL1, SUPRASIL2, SUPRASIL300, SUPRASIL310, HERALUX PLUS, HERALUX-VUV, and the like. In another embodiment, the transmissive portion of the plasma lamp 110 may include, but is not limited to, calcium fluoride, magnesium fluoride, lithium fluoride, crystalline quartz, and crystalline sapphire. A. Schreiber et al., Radiation Resistance of Quartz Glass for VUV Discharge Lamps, J. Phys. D: Appl. Phys. 38 (2005), 3242-3250, is incorporated herein in its entirety, and provides a detailed description of various glasses suitable for implementing the plasma lamp 110 of the present disclosure.

[0047] In one embodiment, the plasma lamp 110 may contain a gas known in the art (e.g., argon, xenon, mercury, etc.) selected to generate a plasma upon absorption of excitation illumination. In one embodiment, when illumination 105 from the illumination source 102 is focused into a volume of gas 109, energy is absorbed by the gas or plasma within the plasma lamp 110 (e.g., through one or more selected absorption lines).

[0048] It is contemplated herein that the system 100 may be utilized to initiate and / or maintain the plasma 111 in a variety of gas environments. In one embodiment, the gas used to initiate and / or maintain the plasma 111 may include an inert gas (e.g., a noble gas or a non-noble gas) or a non-inert gas (e.g., mercury). In another embodiment, the gas used to initiate and / or maintain the plasma 111 may include a mixture of gases (e.g., a mixture of inert gases, a mixture of inert gases and non-inert gases, or a mixture of non-inert gases). For example, gases suitable for implementing the system 100 of the present disclosure may include, but are not limited to, Xe, Ar, Ne, Kr, He, N2, H2O, O2, H2, D2, F2, CH4, one or more metal halides, halogens, Hg, Cd, Zn, Sn, Ga, Fe, Li, Na, Ar:Xe, ArHg, KrHg, XeHg, and mixtures thereof. The present disclosure should be interpreted to extend to any optically excited plasma generating system, and further to any type of gas suitable for sustaining a plasma within a gas containment structure.

[0049] It should be noted that the broadband illumination 114 of the plasma lamp 110 may be coupled with the illumination optics of an optical characterization tool, such as, but not limited to, an inspection tool and / or a metrology tool.

[0050] In one embodiment, system 100 may include various additional optical elements. In one embodiment, the set of additional optical elements may include additional collection optics configured to collect broadband illumination 114 emanating from plasma 111. By way of example, system 100 may include a cold mirror 112 positioned to direct illumination from collection element 108 to a downstream optical element, such as, but not limited to, a homogenizer.

[0051] In another embodiment, another set of optical components may include one or more other lenses (e.g., lenses) disposed along either the illumination path or the collection path of the system 100. The one or more lenses may be utilized to focus illumination from the illumination source 102 within the volume of gas 109. Or, the one or more lenses may be utilized to focus broadband illumination 114 emanating from the plasma 111 onto a selected target (not shown).

[0052] In another embodiment, another set of optical components may include a reflector 106. In one embodiment, the reflector 106 may be positioned to receive illumination 105 from the illumination source 102 and direct the illumination through a focusing element 108 to a volume of gas 109 contained within a plasma lamp 110. In another embodiment, the focusing element 108 is positioned to receive illumination from the mirror 106 and focus the illumination to a focal point of the focusing element 108 (e.g., an elliptical focusing element) where the plasma lamp 110 is located.

[0053] In another embodiment, another set of optical components may include one or more filters (not shown) disposed along either the illumination path or the collection path to filter the illumination before the light enters the plasma lamp 110 or after the light leaves the plasma 111. It should be noted that the set of optical components of system 100 described above and shown in FIG. 1A is set forth merely for purposes of illustration and should not be construed as limiting. It is anticipated that many equivalent optical configurations may be used within the scope of the present invention.

[0054] The subject matter described herein may illustrate other components housed within or connected to other components. It is understood that the architectures depicted are merely illustrative, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components that achieve the same functionality is effectively "associated" to achieve the desired functionality. Thus, any two components combined herein to achieve a particular functionality can be viewed as "associated" with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered as "connected" or "coupled" with each other to achieve the desired functionality, and any two components capable of such association can also be considered as "couplable" with each other to achieve the desired functionality. Examples of what can be coupled include, but are not limited to, physically matchable and / or physically interacting components, and / or wirelessly interactable and / or wirelessly interacting components, and / or logically interacting and / or logically interacting components.

[0055] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes can be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or sacrificing all of its important advantages. The described forms are merely illustrative, and it is intended that the following claims encompass and include such modifications. It will be further understood that the appended claims define the invention.

Claims

1. 1. An illumination source for electrodeless plasma ignition, comprising: one or more ignition lasers configured to ignite a plasma in a gas contained within the plasma lamp; one or more sustaining lasers configured to sustain the plasma; a focusing element for focusing illumination from the sustain laser and the ignition laser onto a gas contained within the plasma lamp, the focusing element having a side port that is a hole for passing illumination from the ignition laser; Including, Illumination from the ignition laser passes through the side port and is then focused by the focusing element and transmitted to the plasma lamp.

1. An illumination source comprising:

2. 10. The illumination source of claim 1, wherein the one or more ignition lasers comprise one or more pulsed lasers.

3. 10. The illumination source of claim 1, wherein the one or more ignition lasers comprise one or more continuous wave lasers operating in a modulated mode.

4. 10. The illumination source of claim 1, wherein the one or more sustain lasers comprise one or more continuous wave lasers.

5. 5. The illumination source of claim 4, wherein the one or more continuous wave lasers include one or more diode lasers.

6. 1. A plasma light source comprising: a plasma lamp containing a volume of gas; one or more ignition lasers; one or more sustain lasers; a focusing element for focusing illumination from the sustain laser and the ignition laser onto a gas contained within the plasma lamp, the focusing element having a side port that is a hole for passing illumination from the ignition laser; the focusing element configured to direct output from the ignition laser and the sustain laser to a volume of gas within the plasma lamp to ignite and sustain a plasma in the volume of gas within the plasma lamp; Illumination from the ignition laser passes through the side port and is then focused by the focusing element and transmitted to the plasma lamp.

1. A plasma light source comprising:

7. 7. The plasma light source of claim 6, wherein the one or more ignition lasers include one or more pulsed lasers.

8. 7. The plasma light source of claim 6, wherein the one or more ignition lasers comprise one or more continuous wave lasers operating in a modulated mode.

9. 7. The plasma light source of claim 6, wherein the one or more sustaining lasers include one or more continuous wave lasers.

10. 10. The plasma light source of claim 9, wherein the one or more continuous wave lasers include one or more diode lasers.

11. 7. The plasma light source of claim 6, wherein the focusing element is configured to focus at least a portion of broadband radiation emitted by the generated plasma and direct the broadband radiation towards one or more further optical elements.

12. 7. The plasma light source of claim 6, wherein the collection element comprises at least one of an ellipsoidal collector mirror, a parabolic collector mirror, or a spherical collector mirror.

13. 7. The plasma light source of claim 6, wherein the plasma lamp comprises a plasma bulb.

14. 14. The plasma light source of claim 13, wherein the plasma bulb has at least one of a cylindrical or spherical shape.

15. 14. The plasma light source of claim 13, wherein the plasma bulb has a cardioid shape.

16. 16. The plasma light source of claim 15, wherein the plasma bulb has a peak disposed on an inner surface of the plasma bulb configured to direct convection currents within the plasma bulb.

17. 7. The plasma light source of claim 6, wherein the plasma lamp is electrodeless.

18. 14. The plasma light source of claim 13, wherein the gas of the plasma bulb comprises at least one of an inert gas, a non-inert gas, or a mixture of two or more gases.

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